Timing Advance Optimization During Uplink Synchronization

This application claims the benefit of Provisional Indian Patent Application No. 202341024646, filed on Mar. 31, 2023, the full disclosure of which is incorporated herein by reference in its entireties for all purposes.

The present disclosure generally relates to the field of wireless communication, and more particularly relates to timing advance optimization during Uplink (UL) synchronization.

A cellular network is a telecommunication interconnection of user devices and cellular Base Station (BS), such as cell tower. A BS includes a service area which is divided into a plurality of cells. A cell defines a geographical area which is served by a transceiver antenna associated with the BS. Multiple user devices present in a particular cell, also referred as serving cell, communicate with the associated transceiver antenna of the BS on a plurality of frequencies and frequency channels.

A Radio Access Network (RAN) is part of the cellular network and is responsible for implementing radio access technology. RANs provide connection to user devices, such as a mobile phone/device, a computer, or any remotely controlled device present in the network, with a Core Network (CN). The user devices may be varyingly known as User Equipment (UE), terminal equipment, Mobile Station (MS), and the like.

While a mobile device, such as a UE, is connected to the serving cell, the mobile device performs measurements of channel parameters and signal parameters related to the serving cell as well as neighbouring cells for a predefined time period. Additionally, when multiple UEs are connected to the serving cell, a distance between the serving BS and the UE is derived through measurements of the time elapsed for radio waves to travel from the UE to the serving BS, known as Timing Advance (TA). Further, the value of the TA may be affected due to the change in the distance between the UE and the serving BS due to the movement of the UE. Similarly, at least one of the neighbouring cells may have an associated TA with respect to the UEs served in the neighbouring cells.

During the movement of the mobile device, the TA, the channel parameters, and the signal parameters related to the serving cell and the neighbouring cells constantly change. For example, if the UE is moving from the coverage area of the serving cell to the coverage area of one of the neighbouring cells, also referred to as target cell, the UE needs to connect to the neighbouring cell and disconnect from the serving cell. This procedure is known as handover (HO). The above-mentioned UE mobility, defining the UE movement, may be referred to as Layer 1 (L1)/Layer 2 (L2) centric inter-cell mobility (LTM). However, it should be understood that the UE mobility may also be realized in a manner alternate to LTM, not discussed herein for the sake of brevity. In LTM, based on the UE movement and in order to perform handover from the serving cell to the target cell, the UE is required to obtain the knowledge of the TA related to the target cell for implementing the same and to continue communicating with the target cell. The knowledge of the TA is necessary for the UE to perform proper synchronization, also referred to as UL synchronization, and connection with the target cell.

In a conventional technique, a disaggregated BS architecture is defined for cellular network. For example, a disaggregated Next Generation Node B (gNB) architecture is defined in 3rd Generation Partnership Project (3GPP) decomposing a gNB into multiple logical entities. For example, the gNB may include a gNB-Control Unit-Control Plane (CU-CP) and the gNB Distributed Unit (DU). Likewise, a single DU may be responsible to host multiple cells. As an example, a single DU may be responsible to host a maximum of 512 cells in current 3GPP specifications. The gNB-CU-CP may host a Packet Data Convergence Protocol (PDCP) and a Radio Resource Control (RRC) layer, while the gNB-DU hosts a Radio Link Control (RLC), a Medium Access Control (MAC), and a Physical (PHY) layer. Further, a downlink (DL) scheduling operation may take place at the gNB-DU. In order to support Layer 1 (L1)/Layer 2 (L2) centric inter-cell mobility, related to the changing of serving cell, in the disaggregated gNB architecture, a mechanism is required in which the handover preparation is performed by the gNB-CU-CP, but handover is executed autonomously by the gNB-DU without further interaction with upper layers, such as PDCP and the RRC layer. The handover preparation may also be referred as target cell configuration preparation. For example, the handover without further interaction with the upper layers may be Random Access Channel (RACH)-less L1/L2 triggered mobility (LTM) Handover (HO).

Short name: NR_Mob_enh2-Core; leading WG: RAN2; 3GPP Release: REL-18; Work item description: RP-221799 Configuration and maintenance for multiple candidate cells to allow fast application of configurations for candidate cells [RAN2, RAN3] Dynamic switch mechanism among candidate serving cells (including SpCell and SCell) for the potential applicable scenarios based on L1/L2 signalling [RAN2, RAN1] L1 enhancements for inter-cell beam management, including L1 measurement and reporting, and beam indication [RAN1, RAN2] To specify mechanism and procedures of L1/L2 based inter-cell mobility for mobility latency reduction: Timing Advance management [RAN1, RAN2] CU-DU interface signaling to support L1/L2 mobility, if needed [RAN3] Note 1: Early RAN2 involvement is necessary, including the possibility of further clarifying the interaction between this bullet with the previous bullet. Note 2: FR2 specific enhancements are not precluded, if any. Note 3: The procedure of L1/L2 based inter-cell mobility are applicable to the following scenarios: Standalone, CA and NR-DC case with serving cell change within one CG. Intra-DU case and intra-CU inter-DU case (applicable for Standalone and CA: no new RAN interfaces are expected) Both intra-frequency and inter-frequency Both FR1 and FR2 Source and target cells may be synchronized or non-synchronized. Notes: L1/L2 triggered mobility is a mobility feature and can be considered a basic UE capability (starting R18). The objectives of the upcoming mobility enhancement Rel. 18 work item can be found in RP-213565: 3GPP Release 18 Work Item (WI) describes further New Radio (NR) mobility enhancements as described below:

TA value of candidate cell is indicated in cell switch command. FFS: whether UE should re-transmit PRACH when reception of RAR is not configured/indicated FFS: how UE determine the transmit power of subsequent PRACH triggered by PDCCH order If reception of RAR is not configured/indicated (without RAR) if RAR is received from candidate cell, whether Type1-PDCCH CSS of the candidate cell is configured to the UE. whether RAR is received from-serving cell or candidate cell content of RAR If reception of RAR is configured/indicated (with RAR), FFS FFS: signaling for configuration/indication of whether RAR needs to be received UE can report the support combination of with RAR only and without RAR only, where support of one default scheme is the baseline UE approach for LTM. Send LS to RAN2 and RAN3 to check the feasibility about this agreement. For PDCCH ordered-RACH for candidate cell(s), RAR reception can be configured/indicated. Note: Definition of candidate cells is up to RAN2 In accordance with the conventional technique, following are the agreements in RAN1 from the RAN1 #112 meeting:

The maximum number of TA values memorized by UE is a UE capability. FFS: whether other parameters such as UE ID, candidate cell ID etc. is contained in RAR If reception of RAR is configured/indicated, RAR contains at least TA of candidate cell.

In the conventional technique, acquiring the target cell TA prior to the serving cell switch, reduces handover latency during an LTM Serving Cell Change (SCC) (also referred hereinafter as Serving Cell Switch), as the TA is already known to the UE and, thus, obtaining the TA can be avoided during the actual SCC. During the LTM, if a UE is configured to perform UL synchronization process, a time window exists between acquiring the target cell TA and execution of the LTM SCC. The time duration may vary from one UE to another UE and even for the same UE on different occasions. Thus, the time duration may not be accurately determined or predicted.

As the UE may undergo mobility during this time duration, as a result the UE's TA at the target cell also undergoes a change. For example, the TA acquired during the UL synchronization process may not be valid at the time of the LTM SCC. Thus, in order to obtain a valid TA at the time of the LTM SCC and to ensure RACH-less LTM Handover, a serving gNB-DU requests the UE to perform the repeated UL synchronization with a target gNB-DU to acquire the updated TA. However, performing the UL synchronization again to acquire the updated TA impacts UE's data transmission at the serving gNB-DU as well as causing an overhead for the target gNB-DU. Alternatively, the serving gNB may request the UE to perform a RACH-based handover at the time of issuing a LTM SCC command, which involves further interaction with upper layers.

Therefore, there is a need for a technique to perform RACH-less handover without the requirement of repeating UL synchronization when a UE undergoes mobility.

The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the disclosure and should not be taken as an acknowledgment or any form of suggestion that this information forms prior art already known to a person skilled in the art.

The present disclosure relates to an apparatus configured to receive, at a User Equipment (UE) from a first distributed unit (DU) of a serving base station, a request to perform an uplink synchronization with a candidate cell of a second DU of a target base station. Further, the apparatus is configured to perform, by the UE, the uplink synchronization by sending a Random Access Channel (RACH) request message to the second DU. Furthermore, the apparatus receives from at least one of the first DU and the second DU by the UE, and based on the uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU, with associated primary timing advance (TA), and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with associated one or more secondary TAs. The apparatus further receives, by the UE, a cell switch command from the first DU indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells. The apparatus is further configured to perform, by the UE, a serving cell switch function to the target beam and apply a corresponding TA associated with the target beam.

The present disclosure also relates to a method for wireless communication at a User Equipment (UE). The method comprises receiving, from a first distribution unit (DU) of a serving base station, a request to perform an uplink synchronization with a second DU of a target base station. Further, the method comprises performing the uplink synchronization by sending a Random Access Channel (RACH) request message to the second DU. Furthermore, the method comprises receiving, from at least one of the first DU and the second DU based on the uplink synchronization, a primary beam identifier of the second DU, with associated primary TA, and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with associated one or more secondary TAs. Moreover, the method comprises receiving a cell switch command from the first DU indicating a target beam of a target cell. The target cell is selected from the primary candidate cell or the one or more secondary candidate cells. The method further comprises performing a serving cell switch function to the target beam and applying a corresponding TA associated with the target beam.

Further, the present disclosure relates to an apparatus configured to determine, at a serving base station and at a first distributed unit (DU) of the serving base station, a candidate cell of a target base station from one or more DUs of one or more candidate base stations, based on one or more signal and channel parameters of a plurality of candidate cells of one or more neighbouring base stations. Further, the apparatus is configured to transmit, from the serving base station, a request, to a User Equipment (UE), to perform uplink synchronization with the candidate cell. Furthermore, the apparatus is configured to receive, at the serving base station and from at least one of the UE and a second DU of the target base station, a primary beam identifier of a primary candidate cell of the second DU with an associated primary timing advance (TA), and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with an associated one or more secondary TAs, the primary beam identifier, the primary TA, the one or more secondary beam identifiers, and the one or more secondary TAs being received by the UE from the the second DU based on the uplink synchronization. Moreover, the apparatus is configured to determine, at the serving base station, a target beam of a target cell from the primary beam identifier and the one or more secondary beam identifiers based on associated one or more signal and channel parameters. The apparatus is further configured to transmit a request, from the serving base station and to the UE to perform serving cell switch function to the target beam and apply a corresponding TA associated with the target beam.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

It should be appreciated by those skilled in the art that any block diagram herein represents conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.

It is to be understood that the present disclosure may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings and described in the following specification are simply exemplary and non-limiting embodiments or aspects. Hence, specific dimensions and other physical characteristics related to the embodiments or aspects disclosed herein are not to be considered as limiting.

In the present document, the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or implementation of the present subject matter described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a device or system or apparatus proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of other elements or additional elements in the device or system or apparatus.

The terms “an embodiment”, “embodiment”, “embodiments”, “the embodiment”, “the embodiments”, “one or more embodiments”, “some embodiments”, and “one embodiment” mean “one or more (but not all) embodiments of the present disclosure” unless expressly specified otherwise.

The terms “including”, “comprising”, “having” and variations thereof mean “including but not limited to” unless expressly specified otherwise.

In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.

Embodiments disclosed herein provide a method and system for acquiring timing advance during UL synchronization and performing optimization to ensure the acquired TA is valid and applicable for a longer duration. A UE sends L1 measurement report (MR) to a serving gNB-DU for configured cells. The serving gNB-DU checks a set Radio Resource Management (RRM) criteria (for example, predefined Reference Signal Received Power (RSRP) threshold) and requests the UE to perform the UL synchronization using a configured Physical Random-Access Channel (PRACH) preamble, with one or more candidate/target cells. The serving gNB-DU uses a Physical Downlink Control Channel (PDCCH) order to request the UE to perform the UL synchronization. The UE performs the UL synchronization and is configured to receive Random Access Response (RAR) from a target gNB-DU which includes a candidate/target cell timing advance to be used by the UE.

In an embodiment, the target gNB-DU includes UE's TA of neighbouring beams in addition to UE's TA of an optimal beam at the candidate/target cell gNB-DU with RAR. This ensures that the UE applies the corresponding TA when one of the neighbouring beam becomes the optimal beam. The neighbouring beams are qualified as any adjacent beam which is anticipated to be accessed by the UE subsequently (i.e., any beam which the UE is expected to move towards with good radio condition).

In an embodiment, the UE, after acquiring the target cell TA during the UL sync procedure, reports the TA of the optimal beam and the neighbouring beams to the serving gNB-DU and at the time of LTM cell switch, the serving gNB-DU indicates the target cell beam to be used by the UE in the serving cell switch command (Downlink Media Access Control-Control Element (DL MAC CE)) and the command is sent to the UE. The UE uses the TA (provided by the candidate/target gNB-DU) corresponding to the beam indicated during the serving cell switch. Alternatively, the UE is autonomously configured to determine the optimal beam belonging to the candidate/target gNB-DU (based on L1 measurements) and apply the corresponding TA (provided by candidate/target gNB-DU). In this alternative, the serving gNB-DU may not provide the target beam Id. Therefore, the proposed method is used to achieve RACH-less HO even with UE mobility post UL synchronization, change of the optimal beam and better TA estimation.

1 FIG. 100 102 102 104 104 104 104 104 106 106 106 106 106 106 106 106 106 106 102 106 106 104 106 106 illustrates a schematic representationof a RAR configuration for a UE, according to the embodiments as disclosed herein. The UEmay be in communication with a serving cell(also referred hereinafter as the serving base stationor the serving gNB-Distributed Unit (DU)as the serving gNB-DUmay include one or more serving cell). For PDCCH ordered RACH for candidate cell(s)A,B (also referred hereinafter as the target base stationA,B or the target/candidate gNB-DUA,B as the target/candidate gNB-DUA,B may include one or more target/candidate cellA,B), the RAR reception is configured/indicated. The RAR configuration may be received at the UEand the RAR may be received either from candidate/target cellA,B or serving cell. In an embodiment, in case of absence of configuration or indication of the reception of the RAR, TA value of candidate cell may be indicated in the cell switch command. In another embodiment, when reception of the RAR is configured/indicated and received from the candidate cellA,B, at least TA may be included in the RAR.

In a conventional disaggregated gNB architecture, a conventional gNB may be decomposed into multiple logical entities, as defined in 3GPP. For example, the conventional gNB may include a gNB-Control Unit-Control Plane (CU-CP) (gNB-Control Unit-Control Plane (CU-CP) is also referred hereinafter as gNB-Centralized Unit (CU) for the sake of brevity) and the gNB DU. Likewise, a single DU may be responsible to host multiple cells. As an example, a single DU may be responsible to host a maximum of 512 cells in current 3GPP specifications. The gNB-CU-CP may host a Packet Data Convergence Protocol (PDCP) and a Radio Resource Control (RRC) layer, while the gNB-DU hosts a Radio Link Control (RLC), a Medium Access Control (MAC), and a Physical (PHY) layer. The scheduling operation takes place at the gNB-DU. In order to support L1/L2 centric inter-cell change, related to the changing of serving cell, in the disaggregated gNB architecture, a mechanism is implemented in which scheduling operation/configuration would take place at the gNB-CU-CP, but executed autonomously by the gNB-DU without any further interaction with the upper layers. For example, the mechanism involves performing the handover preparation by the gNB-CU-CP, but autonomously executing the handover by the gNB-DU without further interaction with upper layers, such as PDCP and the RRC layer.

108 102 108 104 110 104 102 102 In an embodiment, at link, the UEmay send a target cell RSRP MR via linkto the serving cell. In an embodiment, at link, the serving cellmay configure the UEusing the PDCCH order to perform UL synchronization by sending the PRACH preamble, so that the UEacquires the target cell TA.

102 104 106 106 102 106 106 102 104 106 106 102 102 102 In operation, the UEmay be configured to transmit to a first distributed unit (DU) of the serving base station, a measurement report (MR) associated with respective one or more signal and channel parameters of a plurality of candidate cellsA,B of one or more neighbouring base stations. In an example, the UEmay be configured to transmit, to the first DU, L1 MR associated with respective one or more signal and channel parameters of the plurality of candidate cellsA,B associated with the first DU and one or more DUs associated with one or more neighbouring base stations. In an embodiment, the UEmay send Layer 1 (L1) MR to the serving gNB-DUfor the plurality of candidate cellsA,B. In an example, the plurality of candidate cells may include a plurality of non-serving cells. In an example, the UEmay send the MR based on UE's specification and compatibility defining UE's capability, with RAR only and without RAR only, where support of one default scheme may be a baseline UEapproach for the LTM. In an example, a maximum number of TA values that the UEmay be configured to memorize, may define the UE's capability.

104 104 106 106 104 106 106 Further, upon sharing the MR to the serving base station, the first DU of the serving base stationmay determine a candidate cell of a target base stationA,B from one or more DUs of one or more candidate base stations. NOTE: The candidate cell could belong to the same base station as the serving cell as well. In an embodiment, the target bases station may be the serving base station. In another embodiment, the determination of the candidate cell may be based on one or more signal and channel parameters of a plurality of candidate cells of the one or more neighbouring base stations. In an embodiment, upon receiving the MR, the serving gNB-DUmay check the set RRM criteria. In an example, the RRM criteria may be a predefined RSRP threshold. Based on the determination of the target base stationA,B, the first DU may transmit a request, to the UE, to perform uplink synchronization with the determined candidate cell.

102 104 106 106 104 102 102 102 102 106 106 Accordingly, the UEmay receive a request from the first DU of the serving base stationto perform the uplink synchronization with the candidate cell of a second DU associated with the target base stationA,B. In an example, the first DU of the serving base stationmay transmit the request to perform the uplink synchronization to the UEusing a PDCCH order. Further, the UEmay perform the uplink synchronization by sending a Random Access Channel (RACH) request message to the second DU. In an embodiment, in response to performing the uplink synchronization, the UEmay be configured to receive, from one of the first DU and the second DU, a Random-Access Response (RAR). For example, the RAR may include at least the primary beam identifier of a primary candidate cell of the second DU with the associated primary TA, and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with one or more associated secondary TAs. The secondary beam identifiers may be determined or selected based on respective signal quality metrics. For another example, the UEmay be configured to receive the RAR as a subsequent message received from the target base stationA,B. The RAR may include at least the primary beam identifier with the associated primary TA, and one or more secondary beam identifiers with one or more associated secondary TAs.

102 106 106 106 106 102 106 106 104 102 106 106 In an embodiment, based on the uplink synchronization, the UEmay receive from the target base stationA,B, a primary beam identifier of the target base stationA,B, with associated primary timing advance (TA). Additionally, the UEmay also receive one or more secondary beam identifiers of the target base stationA,B with associated one or more secondary TAs. In an alternative embodiment, the first DU of the serving base stationmay receive the primary beam identifier of the primary candidate cell of the second DU with an associated primary TA, and the one or more secondary beam identifiers of the one or more secondary candidate cells of the second DU with an associated one or more secondary TAs, from one of the UEand the second DU of the target base stationA,B.

102 112 102 112 112 112 102 In an embodiment, the UEmay include an optimal beam determination moduleA. The UEmay utilize the optimal beam determination moduleA to determine an optimal beam from the primary beam identifier and one or more secondary beam identifiers and define the optimal beam as the target beam. In an embodiment, the optimal beam determination moduleA determines the optimal beam based on comparison between one or more signal and channel parameters associated with the primary beam identifier with corresponding one or more signal and channel parameters associated with at least one of the secondary beam identifiers. Based on the comparison, the optimal beam determination moduleA may determine the target beam from the primary beam identifier and the one or more secondary beam identifiers. Further, the UEmay perform a serving cell switch function to the target beam and apply a corresponding TA associated with the target beam.

102 104 106 106 106 106 104 112 104 112 104 104 104 106 106 104 In another embodiment, the UEmay transmit to the serving base station, the primary beam identifier of the target base stationA,B with an associated primary timing advance (TA), and one or more secondary beam identifiers of the target base stationA,B with an associated one or more secondary TAs. In an example, the serving base stationmay include the optimal beam determination moduleB. Thereafter, the serving base stationmay utilize the optimal beam determination moduleB to determine an optimal beam from the primary beam identifier and the one or more secondary beam identifiers based on associated one or more signal and channel parameters and define the optimal beam as the target beam. In an example, to determine the optimal beam, the serving base stationmay be configured to compare one or more signal and channel parameters associated with the primary beam identifier with corresponding one or more signal and channel parameters associated with at least one of the secondary beam identifiers. In an embodiment, serving base stationmay be configured to determine, at the first DU of the serving base station, a candidate cell of the target base stationA,B from one or more DUs of one or more candidate base stations, based on one or more signal and channel parameters of a plurality of candidate cells of one or more neighbouring base stations. The serving and target base stations could be the same base station as well. Further, the serving base stationmay be configured to determine the target beam from the primary beam identifier and the one or more secondary beam identifiers based on the comparison result.

102 102 102 In an example, the optimal beam may be defined as the beam having an optimal TA at a particular period of time. Therefore, by including TA of the neighbouring beams along with the target beam, it is ensured that the UEapplies the corresponding TA when any of the neighbouring beams becomes the optimal beam. The neighbouring beams may qualify as any adjacent beam that can be anticipated to be accessed by the UEsubsequently. For example, the neighbouring beams are beams which the UEcan be expected to move towards and having optimal channel and signal characteristics.

104 102 102 Subsequently, the serving base stationmay request the UEto perform serving cell switch function to the target beam based on a corresponding TA associated with the target beam. In an example, the first DU may transmit a cell switch command to the UEindicating a target beam of a target cell. In an example, the cell switch command may be a Layer 1/Layer 2 Triggered Mobility (LTM) cell switch command. In an example, the target cell may be selected from the primary candidate cell or the one or more secondary candidate cells.

104 102 106 106 102 106 106 102 102 Subsequently, the serving gNB-DUmay request the UEto perform UL synchronization using the configured PRACH preamble, with one or more target cellsA,B. The UEmay perform the UL synchronization and receive RAR from the target gNB-DUA,B which includes the candidate/target cell TA to be used by the UE. Accordingly, the UEmay use the candidate/target cell TA to perform RACH-less LTM handover.

2 FIG. 102 106 106 106 106 is a sequence diagram illustrating a scenario in which the UEdetermines an optimal beam belonging to the target gNB-DUA,B (based on L1 measurements) and applies the corresponding TA provided by the target gNB-DUA,B, according to the embodiments as disclosed herein.

2 FIG. 102 106 106 Referring to, the UEis configured to determine an optimal beam belonging to the target gNB-DUA,B (based on L1 measurements) and apply the corresponding TA.

201 102 104 At step S, the UEis still connected to the serving gNB-DU(before the LTM Serving cell switch).

202 102 200 200 At step S, the UEuses the RRC connection with a gNB-Centralized Unit (CU) () and sends L3 RRC measurements to the gNB-CU.

203 200 At step S, the gNB-CUdecides to prepare inter-gNB-DU LTM candidate cell.

204 200 106 106 At step S, the gNB-CUinitiates the UE context setup request message to the target gNB-DUA,B through F1 interface, to prepare an inter-DU LTM candidate cell.

205 106 106 At step S, the target gNB-DUA,B acknowledges with UE context setup response message through F1 interface and provides the candidate/target cell configuration.

206 200 104 At step S, the gNB-CUsends DL RRC message transfer (RRC reconfiguration (LTM target cell configuration)) to the serving gNB-DUthrough F1 interface.

207 102 104 106 106 At step S, the RRC reconfiguration message is passed to the UE. The serving gNB-DUchecks the set of RRM criteria (for example: predefined RSRP threshold) set to trigger sending the L1 measurements to the target gNB-DUA,B.

208 102 104 At step S, the UEsends L1 measurements of the configured cells to the serving gNB-DU.

208 209 104 102 Based on step S, at step S, the serving gNB-DUrequests the UEto perform the UL synchronization using the configured PRACH preamble, with one or more target cells.

210 104 102 At step S, the serving gNB-DUuses the PDCCH order to request the UEto perform the UL sync.

211 102 106 106 At step S, the UEperforms the UL synchronization and sends the RACH Preamble to the target gNB-DUA,B cell.

212 102 106 106 102 106 106 102 At at step S, the UEis configured to receive the RAR from the target gNB-DUA,B which includes the candidate/target cell TA to be used by the UE. The target gNB-DUA,B also transmits multiple neighbouring beams with timing advance to the UEin the RAR.

213 102 At step S, the TA corresponding to multiple beams of the candidate/target cell are available and stored at the UE.

214 102 104 At step S, the UEsends the TAs of the target cell by an Uplink Media Access Control-Control Element (UL MAC CE) to the serving gNB-DU.

215 102 104 102 104 At step S, the UEsends intra-frequency L1 Measurement report to the serving gNB-DUafter receiving the RAR. In an embodiment, the UEmay send L1 MR to the serving gNB-DUfor the configured cells.

216 104 102 At step S, the serving gNB-DUdetermines the optimal beam of the target cell for the UEusing the corresponding TA.

217 104 102 At step S, the serving gNB-DUsends the optimal beam of the target cell by the MAC CE to the UE.

218 102 106 106 At step S, the UEsends the RACH-Less HO to the target gNB-DUA,B cell.

3 FIG. 102 106 106 106 106 is a sequence diagram illustrating another scenario in which the UEdetermines an optimal beam belonging to the target gNB-DUA,B (based on L1 measurements) and applies the corresponding TA provided by the target gNB-DUA,B, according to the embodiments as disclosed herein.

3 FIG. 102 106 106 Referring to, the UEdetermines an optimal beam belonging to the target gNB-DUA,B (based on L1 measurements) and apply the corresponding TA.

301 102 104 At step S, the UEis still connected to the serving gNB-DU(before the LTM Serving cell switch).

302 102 200 200 At step S, the UEuses the RRC connection with the gNB-CUand sends L3 RRC measurements to the gNB-CU.

303 200 At step S, the gNB-CUdetermines to prepare inter-gNB-DU LTM candidate cell.

304 200 106 106 At step S, the gNB-CUinitiates the UE context setup request message to the target gNB-DUA,B to prepare an inter-DU LTM candidate cell.

305 106 106 At step S, the target gNB-DUA,B acknowledges with UE context setup response message and provides the candidate/target cell configuration.

306 200 104 At step S, the gNB-CUsends DL RRC message (RRC reconfiguration (LTM target cell configuration)) to the serving gNB-DUthrough F1 interface.

307 102 104 106 106 At step S, the RRC reconfiguration message is passed to the UE. The serving gNB-DUchecks the set of RRM criteria (for example: predefined RSRP threshold) set to trigger sending the L1 measurements to the target gNB-DUA,B.

308 102 104 At step S, the UEsends L1 measurements of the configured cells to the serving gNB-DU.

308 309 104 102 Based on step S, at step S, the serving gNB-DUrequests the UEto perform the UL synchronization using the configured PRACH preamble, with one or more target cells.

310 104 102 At step S, the serving gNB-DUuses the PDCCH order to request the UEto perform the UL sync.

311 102 At step S, the UEperforms the UL synchronization and sends the RACH Preamble to the target gNB-DU cell.

312 102 106 106 At at step S, the UEis configured to receive the RAR from the target gNB-DUA,B.

313 106 106 104 200 102 106 106 At step S, the target gNB-DUA,B initiates a context modification procedure to notify the serving gNB-DUof the candidate/target cell TAs. An indication that the UE context modification is required, is sent to the gNB-CU. Such indication includes the candidate/target cell TA to be used by the UE. The target gNB-DUA,B also includes multiple beams with timing advance, in the F1 message.

314 312 200 At step S, based on the indications described at step S, the gNB-CUsends an acknowledgment related to the indication that the UE context modification is required.

315 200 104 102 200 106 106 104 At step S, the gNB-CUinitiates the UE context modification request message to the serving gNB-DU. This includes the candidate/target cell TA to be used by the UE. The gNB-CUalso includes multiple beams with timing advance sent by target gNB-DUA,B to the serving gNB-DUin the F1 message.

316 104 At step S, the serving gNB-DUacknowledges with UE context modification request message through F1 interface.

317 104 At step S, the TA corresponding to multiple beams of the target cell are available and stored at the serving gNB-DU.

318 102 104 At step S, the UEsends intra-frequency L1 Measurement report to the serving gNB-DUbased on the reception of the RAR.

319 104 102 At step S, the serving gNB-DUdetermines the optimal beam of the target cell for the UEand uses the corresponding TA.

320 104 102 At step S, the serving gNB-DUsends the target beam of the target cell by the MAC CE to the UE, based on the determination of the optimal beam.

321 102 106 106 At step S, the UEsends the RACH-Less HO to the target gNB-DUA,B cell.

4 FIG. 400 illustrates a flowchart of a methodfor wireless communication at a UE, according to the embodiments as disclosed herein.

4 FIG. 400 400 As illustrated in, methodmay comprise one or more steps. The methodmay be described in the general context of computer executable instructions. Generally, computer executable instructions can include routines, programs, objects, components, data structures, procedures, modules, and functions, which perform particular functions or implement particular abstract data types.

400 The order in which methodis described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method. Additionally, individual blocks may be deleted from the methods without departing from the scope of the subject matter described herein. Furthermore, the method can be implemented in any suitable hardware, software, firmware, or combination thereof.

402 102 104 106 106 102 104 104 102 104 At step, the UEmay receive a request, from the first distribution unit (DU) of the serving base station, to perform an uplink synchronization with the second DU of the target base stationA,B. In an embodiment, the UE, prior to receiving from the serving base station, the request to perform the uplink synchronization, may transmit, to the serving base station, a measurement report (MR) associated with respective one or more signal and channel parameters of a plurality of candidate cells of one or more neighbouring base stations. In an example, the plurality of candidate cells may include a plurality of non-serving cells. In an embodiment, the UEreceives the request to perform uplink synchronization using a PDCCH order sent by the serving base station.

404 102 102 106 106 At step, the UEmay perform the uplink synchronization by sending a Random Access Channel (RACH) request message to the second DU. In an embodiment, the UEmay receive, from the target base stationA,B and in response to performing the uplink synchronization, a Random-Access Response (RAR). For example, the RAR may include at least the primary beam identifier with the associated primary TA, and one or more secondary beam identifiers with one or more associated secondary TAs.

406 102 At step, the UEmay receive one of the first DU and the second DU based on the uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU, with associated primary timing advance (TA), and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with associated one or more secondary TAs.

408 102 102 At step, the UEmay receive a cell switch command from the first DU indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells. In another embodiment the UEmay receive a target beam from the primary beam identifier and one or more secondary beam identifiers. In an embodiment, the determination of the target beam may be performed by comparing one or more signal and channel parameters associated with the primary beam identifier with corresponding one or more signal and channel parameters associated with at least one of the secondary beam identifiers. Subsequently, a target beam may be determined from the primary beam identifier and the one or more secondary beam identifiers based on the comparison result. In an example, the one or more secondary beam identifiers are determined based on respective signal quality metrics. For example, a beam may be selected as a secondary beam based on the measurement of the signal quality metrics associated with the beam as compared to other beams present in a beam group.

410 102 At step, the UEmay perform a serving cell switch function to the target beam and apply the corresponding TA associated with the target beam.

106 106 102 106 106 102 104 104 106 106 106 106 In the proposed method, the target gNB-DUA,B adds the UE's TA of optimal beam in the RAR (optimal beam or the DL beam corresponding to the UL beam that is used by the UEto perform UL synchronization operation). Further, the target gNB-DUA,B includes the UE's TA of neighbouring beams. Thereby ensuring that in case of any of the neighbouring beams becoming the optimal beam, the UEmay dynamically apply the corresponding TA to the optimal beam. Therefore, such dynamic application of the corresponding TA may allow to reduce the overall time taken to perform handover from the serving base stationor cellto the target base stationA,B or target cellA,B. Such dynamic application of the corresponding TA also eliminate the requirement to repeated perform UL synchronization to obtain updated TA due to the UE's mobility.

102 102 102 104 106 106 In an embodiment, the neighbouring beams are qualified as any adjacent beam which may be anticipated to be accessed by the UEsubsequently, such as, any beam which the UEis expected to move towards and has optimal channel and signal parameters or characteristics. In an example, the qualification of the neighbouring beams may be interpreted or computed using Artificial Intelligence (AI)-Machine Learning (ML) methods. For example, to determine the qualification of the neighbouring beams a priority list may be generated by the UEor the serving base station. In another example, the priority list of the neighbouring beams may be generated at the target base stationA,B.

102 102 200 In an embodiment, the priority list of neighbouring beams may be generated based on a target beam/beam-group selected by UEon one or more previous occasions of handover. In an example, the priority list may be generated based on one or more of beamforming structure being implemented in the cell, total number of neighbouring target beams/beam-groups available from an optimal beam or beam group, or RSRP metrics reported by UEfor the different beams/beam-groups. In another embodiment, the number of neighbouring beam TAs may be decided by the gNB-CU.

104 102 102 102 106 106 In an embodiment, the serving gNB-DUmay indicate the target cell beam to be used by the UE, in the SCC command, such as Downlink (DL) MAC CE, sent to the UE. The UEmay use the TA which is being provided by the target gNB-DUA,B corresponding to the beam indicated during SCC command.

102 106 106 106 106 In another embodiment, the UEis autonomously configured to determine the optimal beam belonging to the target gNB-DUA,B (based on L1 measurements) and apply the corresponding TA (provided by the target gNB-DUA,B).

104 104 106 106 In the proposed method and system, the serving gNB-DUrefines the optimal beam to correct for UE mobility and implement better TA estimation. In an embodiment, a receiver architecture associated with a digital beamforming reception is implemented by the proposed method and system. In another embodiment, an analog beamforming reception is implemented by the proposed method and system. The proposed method is used to receive a Physical Random Access Channel (PRACH) signal with multiple receive beams (a set of beams adjacent to each other, list given by the serving cellor chosen by the target cellA,B) are processed.

106 106 104 106 106 102 With at least one of the receive beams, the target gNB-DUA,B may compute the TA. In an example, the serving cellmay share the TA using the UL MAC CE which includes both beam index of the target cellA,B and corresponding TA by using the UE.

102 102 102 102 104 102 106 106 102 102 As the UEwill have the information of the TAs of neighbouring or secondary beams apart from the information of the TA of the target beam, the UEmay be capable of determining if the target beam is the optimal beam to perform the handover. If the UEdetermines that one of the secondary beams is the optimal beam to perform the handover, the UEcan accordingly select the secondary beam and replace with the target beam. In an alternate embodiment, the serving base stationmay also be configured to compare the target beam with the secondary beams to determine an optimal beam and accordingly transmit the optimal beam information to the UE. Therefore, the UEmay be able to perform RACH-less LTM handover with a target base stationA,B with the optimal beam which is valid for an extended time period even when the UEundergoes mobility. For example, when the UEtravels from one location to another, thereby causing change in the TA.

5 FIG. 5 FIG. 500 500 500 102 500 104 500 502 504 508 510 512 514 502 514 504 514 502 504 506 508 506 510 512 514 illustrates a detailed block diagram of an apparatuswherein the method for wireless communication may be implemented.illustrates a detailed block diagram of an apparatus, in accordance with some embodiments of the present disclosure. In one embodiment it will be appreciated that the apparatusis associated with the UE. In another embodiment it will be appreciated that the apparatusis associated with the serving base station. The apparatusmay comprise at least one transmitter, at least one receiver, at least one processor, at least one memory, at least one interface, and at least one antenna. The at least one transmittermay be configured to transmit data/information to one or more nodes/devices using the antennaand the at least one receivermay be configured to receive data/information from the one or more nodes/devices using the antenna. The at least one transmitterand receivermay be collectively implemented as a single transceiver module. In one non-limiting embodiment, the at least one processormay be communicatively coupled with the transceiver module, memory, interface, and antennafor implementing the above-described technique of processing the wireless communication and specifically performing RACH-less LTM HO.

508 510 508 510 508 510 The at least one processormay include, but not restricted to, one or more of microprocessors, microcomputers, micro-controllers, central processing units, state machines, logic circuitries, and any devices that manipulate signals based on operational instructions. A processor may also be implemented as a combination of computing devices, e.g., a combination of a plurality of microprocessors or any other such configuration. The at least one memorymay be communicatively coupled to the at least one processorand may comprise various instructions, the UE signal strength data, the initial bandwidth part, the one or more dedicated bandwidth parts, the pre-defined intervals, and the like. The at least one memorymay include one or more of a Random-Access Memory (RAM) unit and a non-volatile memory unit such as a Read Only Memory (ROM), optical disc drive, magnetic disc drive, flash memory, Electrically Erasable Read Only Memory (EEPROM), a memory space on a server or cloud and so forth. The at least one processormay be configured to execute one or more instructions stored in the memory.

512 500 500 The interfacesmay include a variety of software and hardware interfaces, for example, a web interface, a graphical user interface, an Input Device-Output Device (I/O) interface, a network interface, and the like. The I/O interfaces may allow the apparatusto communicate with one or more nodes/devices either directly or through other devices. The network interface may allow the apparatusto interact with one or more networks either directly or via any other network.

500 112 112 The apparatusmay further include the optimal beam determination moduleA,B to determine an optimal beam from the primary beam identifier and the one or more secondary beam identifiers based on associated one or more signal and channel parameters and define the optimal beam as the target beam. In an example, the optimal beam is the target beam based on the determination that the current target beam has optimal characteristics as compared to other beam or beam group.

102 102 106 106 102 106 106 106 106 The UE, when provided with TAs of the neighbouring beams along with the TA of the target beam, allows the UEto autonomously determine the optimal beam belonging to the target gNB-DUA,B. For example, the UEmay be autonomously configured to consider the channel and signal parameters, such as L1 measurements, to determine the optimal beam belonging to the target gNB-DUA,B and, subsequently, apply the corresponding TA provided by the target gNB-DUA,B.

102 104 106 106 102 102 102 102 In an embodiment [1], an apparatus is configured to: receive, at a User Equipment (UE)from a first distributed unit (DU) of a serving base station, a request to perform an uplink synchronization with a candidate cell of a second DU of a target base stationA,B; perform, at the UE, the uplink synchronization by sending a Random Access Channel (RACH) request message to the second DU; receive, from one of the first DU and the second DU and at the UE, based on the uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU, with associated primary timing advance (TA), and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with associated one or more secondary TAs; receive, at the UE, a cell switch command from the first DU indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells; and perform, at the UE, a serving cell switch function to the target beam and apply a corresponding TA associated with the target beam.

102 In an embodiment [2], prior to receiving, from the first DU, the request to perform the uplink synchronization, the apparatus described in the embodiment [1] is configured to: transmit, from the UEand to the first DU, a Layer 1 measurement report (L1 MR) associated with respective one or more signal and channel parameters of a plurality of candidate cells associated with the first DU and one or more DUs associated with one or more neighbouring base stations, wherein the plurality of candidate cells includes a plurality of non-serving cells.

102 In an embodiment [3], in response to performing the uplink synchronization, the apparatus described in the embodiment [1] is configured to receive, at the UEand from the second DU, a Random Access Response (RAR), wherein the RAR includes at least the primary beam identifier with the associated primary TA, and one or more secondary beam identifiers with one or more associated secondary TAs.

In an embodiment [4], the cell switch command associated with the apparatus described in the embodiment [1] is a Layer 1/Layer 2 Triggered Mobility (LTM) cell switch command.

In an embodiment [5], according to the apparatus described in the embodiment [1], the one or more secondary beam identifiers are determined based on respective signal quality metrics.

102 In an embodiment [6], according to the apparatus described in the embodiment [1], the request to perform the uplink synchronization is received at the UEusing a Physical Downlink Control Channel (PDCCH) order, and wherein the serving base station is the target base station.

102 104 106 106 In an embodiment [7], a method for wireless communication at a User Equipment (UE)is performed. The method comprising: receiving, from a first distribution unit (DU) of a serving base station, a request to perform an uplink synchronization with a second DU of a target base stationA,B; performing the uplink synchronization by sending a Random Access Channel (RACH) request message to the second DU; receiving, from at least one of the first DU and the second DU based on the uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU, with associated primary timing advance (TA), and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with associated one or more secondary TAs; receiving a cell switch command from the first DU indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells; and performing a serving cell switch function to the target beam and apply the corresponding TA associated with the target beam.

In an embodiment [8], according to the method described in the embodiment [7], prior to receiving, from the first DU, the request to perform the uplink synchronization, transmitting, to the first DU, a Layer 1 measurement report (L1 MR) associated with respective one or more signal and channel parameters of a plurality of candidate cells associated with the first DU and one or more DUs associated with one or more neighbouring base stations, wherein the plurality of candidate cells includes a plurality of non-serving cells.

In an embodiment [9], the method described in the embodiment [7] further comprises: receiving, from the second DU and in response to performing the uplink synchronization, a Random Access Response (RAR), wherein the RAR includes at least the primary beam identifier with the associated primary TA, and one or more secondary beam identifier with one or more associated secondary TAs.

In an embodiment [10], the method described in the embodiment [7] further comprises: determining the one or more secondary beam identifiers by determining the one or more secondary beam identifiers based on respective signal quality metrics.

In an embodiment [11], according to the method described in the embodiment [7], receiving the request to perform the uplink synchronization include receiving the request to perform the uplink synchronization using a Physical Downlink Control Channel (PDCCH) order, and wherein the serving base station is the target base station.

104 104 106 106 104 102 104 102 106 106 104 104 102 In an embodiment [12], an apparatus is configured to: determine, at a serving base stationand at a first distributed unit (DU) of the serving base station, a candidate cell of a target base stationA,B from one or more DUs of one or more candidate base stations, based on one or more signal and channel parameters of a plurality of candidate cells of one or more neighbouring base stations; transmit, from the serving base station, a request, to a User Equipment (UE), to perform uplink synchronization with the candidate cell; receive, at the serving base stationand from at least one of the UEand a second DU of the target base stationA,B, a primary beam identifier of a primary candidate cell of the second DU with an associated primary timing advance (TA), and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with an associated one or more secondary TAs, the primary beam identifier, the primary TA, the one or more secondary beam identifiers, and the one or more secondary TAs being received from the second DU based on the uplink synchronization; determine, at the serving base station, a target beam of a target cell from the primary beam identifier and the one or more secondary beam identifiers based on associated one or more signal and channel parameters; and transmit a request, from the serving base station, the UEto perform serving cell switch function to the target beam and apply a corresponding TA associated with the target beam.

104 104 In an embodiment [13], according to the apparatus described in the embodiment [12], to determine the target beam, the apparatus is configured to: compare, at the serving base station, one or more signal and channel parameters associated with the primary beam identifier with corresponding one or more signal and channel parameters associated with each of the one or more secondary beam identifiers; and based on the comparison, determine, at the serving base station, the target beam from the primary beam identifier and the one or more secondary beam identifiers.

104 102 In an embodiment [14], the apparatus described in the embodiment [12] is further configured to: prior to determining the second DU, receive, at the serving base stationand from the UE, a Layer 1 measurement report (L1 MR) associated with respective one or more signal and channel parameters of the plurality of candidate cells associated with the first DU and one or more DUs associated with one or more neighbouring base stations, wherein the plurality of candidate cells includes a plurality of non-serving cells.

104 In an embodiment [15], the apparatus described in the embodiment [12] is configured to transmit, from the serving base station, the request to perform the uplink synchronization that comprises a request for a Random Access Channel Request (RACH), to the second DU, wherein the request for the RACH triggers a Random Access Response (RAR) from second DU including at least the primary beam identifier with the associated primary TA, and the one or more secondary beam identifiers with the associated one or more secondary TAs.

In an embodiment [16], according to the apparatus described in the embodiment [14], the serving cell switch function is performed based on a Layer 1/Layer 2 Triggered Mobility (LTM) cell switch command.

In an embodiment [17], the apparatus described in the embodiment [12] determines the one or more secondary beam identifiers based on respective signal quality metrics.

102 In an embodiment [18], the apparatus described in the embodiment [12] transmits the request to perform the uplink synchronization to the UE () using a Physical Downlink Control Channel (PDCCH) order, and wherein the serving base station is the target base station.

102 104 106 106 In an embodiment [19], a non-transitory computer-readable medium having program instructions stored thereon, executed by an apparatus for wireless communication at a User Equipment (UE), is disclosed. The program instructions may comprise receiving, from a first distribution unit (DU) of a serving base station, a request to perform an uplink synchronization with a second DU of a target base stationA,B; performing the uplink synchronization by sending a Random Access Channel (RACH) request message to the second DU; receiving, from one of the first DU and the second DU based on the uplink synchronization, a primary beam identifier of a primary candidate cell of the second DU, with associated primary timing advance (TA), and one or more secondary beam identifiers of at least one of the primary candidate cell and one or more secondary candidate cells of the second DU with associated one or more secondary TAs; receiving a cell switch command from the first DU indicating a target beam of a target cell, wherein the target cell is selected from the primary candidate cell or the one or more secondary candidate cells; and performing a serving cell switch function to the target beam and apply the corresponding TA associated with the target beam.

In an embodiment [20], according to the non-transitory computer-readable medium described in the embodiment [19], the program instructions may comprise determining the target beam comprises: comparing one or more signal and channel parameters associated with the primary beam with corresponding one or more signal and channel parameters associated with each of the one or more secondary beams; and based on the comparison, determining a target beam from the primary beam and the one or more secondary beams.

In an embodiment [21], according to the non-transitory computer-readable medium described in the embodiment [19] the program instructions may comprise: prior to receiving, from the first DU, the request to perform the uplink synchronization, transmitting, to the first DU, a Layer 1 measurement report (L1 MR) associated with respective one or more signal and channel parameters of a plurality of candidate cells associated with the first DU and one or more Dus associated with one or more neighbouring base stations, wherein the plurality of candidate cells includes a plurality of non-serving cells.

In an embodiment [22], according to the non-transitory computer-readable medium described in the embodiment [19] the program instructions may comprise: receiving, from the second DU and in response to performing the uplink synchronization, a Random Access Response (RAR), wherein the RAR includes at least the primary beam identifier with the associated primary TA, and one or more secondary beam identifier with one or more associated secondary TAs.

In an embodiment [23], according to the non-transitory computer-readable medium described in the embodiment [19], the program instructions may comprise determining the one or more secondary beam identifiers by determining the one or more secondary beam identifiers based on respective signal quality metrics.

500 104 In an embodiment [24], according to the non-transitory computer-readable medium described in the embodiment [19], the program instructions may comprise receiving the request to perform uplink synchronization include receiving the request to perform uplink synchronization using a PDCCH order. In one non-limiting embodiment, the apparatusmay be a part of the serving base station, but not limited thereto.

500 102 In another non-limiting embodiment, the apparatusmay be a part of the UE, but not limited thereto.

510 508 508 In a non-limiting embodiment of the present disclosure, one or more non-transitory computer-readable media may be utilized for implementing the embodiments consistent with the present disclosure. A computer-readable medium refers to any type of physical memory (such as the memory) on which information or data readable by a processor may be stored. Thus, a computer-readable media may store one or more instructions for execution by the at least one processor, including instructions for causing the at least one processorto perform steps or stages consistent with the embodiments described herein. The term “computer-readable media” should be understood to include tangible items and exclude carrier waves and transient signals. By way of example, and not limitation, such computer-readable media can comprise Random Access Memory (RAM), Read-Only Memory (ROM), volatile memory, non-volatile memory, hard drives, Compact Disc (CD) ROMs, Digital Video Disc (DVDs), flash drives, disks, and any other known physical storage media.

Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer readable media having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. For certain aspects, the computer program product may include packaging material.

The various illustrative logical blocks, modules, and operations described in connection with the present disclosure may be implemented or performed with a general-purpose processor, discrete gate or transistor logic, discrete hardware components or any combination thereof designed to perform the functions described herein. A general-purpose processor may include a microprocessor, but in the alternative, the processor may include any commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a plurality of microprocessors, or any other such configuration.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.